The present invention is in the field of metal joining by means of brazing using a brazing alloy to join the two parts together.
Brazing technology currently uses tapes, paste, or powder as the joining medium.
Brazing tape is a dispersion of brazing alloy in an organic vehicle which carries the alloy to the point of joining and is ideally suited to joining flat structures such as honeycomb to sheet or sheet to sheet or extrusion to sheet or Honeycomb. Brazing tape can be supplied with an adhesive coating which will hold the matrix of organic binder and braze metal to one surface while the temperature of the entire structure is raised to burn off the organic component and eventually liquify the brazing alloy to effect the bond.
Brazing tape does not work well when the metals to be joined are mechanically fitted together and need a seal on an irregular surface as when a pair of nesting concentric rings are bonded together. The tape cannot usually be slit narrow enough to fit into the crevices which may have irregular 0.040" to 0.060" openings.
Brazing paste or powder has been used to seal narrow openings with the result that the braze joint may have voids due to uneven application of the paste or poor distribution of the powder. Voids often require a second application of either paste or powder and a second firing of the part to braze the joint.
Brazing paste is a dispersion of braze powders in a liquid vehicle which is usually water based.
Brazing paste is supplied in tubes or cartridges for application by a pressure gun usually powered by compressed air.
The diameter of the orifice through which the paste is delivered, the air pressure used, and the speed at which the gun is moved over the work pieces determines the size of the extruded bead and its uniformity.
With brazing paste as the joining medium, viscosity is critical and a thin paste or a high ambient temperature at the time of application may cause excessive flow within the joint and lead to starved areas which could result in weak spots, leaks, or burn through.
A high viscosity paste will usually not flow evenly at ambient temperatures and may not penetrate deep enough into a narrow joint (0.030" to 0.060") leaving a gap or void. Paste is hard to apply evenly to large parts with long sections or large diameters.
Brazing pastes have limited working life and may lose application properties on aging in both bulk and cartridge. These application properties are a result of change in viscosity and are usually not reversible.
Brazing powders can be applied by physically spreading the material over an adhesive layer manually or spraying the powder over the parts by means of a spray gun which will provide a more even distribution of alloy. More than one application is usually necessary to deposit sufficient alloy.
Brazing powders used in narrow joints are usually dependent upon the application of an adhesive to the joint and its ability to accumulate sufficient powder which when melted will fill the joint and any voids, to provide a good seal and form a strong bond. Most brazing powder joints do not have an even distribution of alloy and are very prone to voids and weak spots.
It is a principal object of this invention to provide a material produced by an extrusion process which can be used to join metals together which is uniform in structure or matrix and can be easily applied to the parts to be joined.
It is a further object of this invention to provide this joining material produced by an extrusion process in a shape or shapes to allow for ease of application and taylored to the joint which must be made.
It is a further object of this invention to impart to these extruded joining materials physical properties such as tensile strength, elongation, handling ease, and storage life not available in present tape, paste, or powder.
It is a further object of this invention to produce a shape or configuration which can be used to separate or stop flowing braze alloy by replacing the metal component with an inorganic pigment of appropriate composition.
A further object of this invention is to provide a procedure for fabricating shapes by extrusion different from conventional materials which are brazing tapes, pastes, and powder slurries of deposits.
A further object of this invention is to provide by extrusion a braze shape such as a cylindrical bead or a rectangular strip or other configuration by incorporating a polymer backbone binder which will produce the shape and impart desirable physical properties making the shape a dimensionally stable product.
Other objects and advantages of the invention will become apparent from the following descriptions thereof.